Low profile multi-IC chip package connector

ABSTRACT

A low profile multi-IC chip package for high speed application comprises a connector for electrically connecting the equivalent outer leads of a set of stacked primary semiconductor packages. In one embodiment, the connector comprises a two-part sheet of flexible insulative polymer with buses formed on one side. In another embodiment, the connector comprises multiple buses formed from conductive polymer. In further embodiments, the primary packages are stacked within a cage and have their outer leads in unattached contact with buses within the cage or, alternatively, are directly fixed to leads or pads on the host circuit board.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/792,771, filed Feb. 23, 2001, pending, which is a continuation ofapplication Ser. No. 09/349,522, filed Jul. 8, 1999, now U.S. Pat. No.6,258,623 B1, issued Jul. 10, 2001, which is a continuation ofapplication Ser. No. 09/138,372, filed Aug. 21, 1998, now U.S. Pat. No.6,153,929, issued Nov. 28, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to semiconductor deviceassemblies having molded housings. More particularly, the inventionrelates to connectors for joining a stack of packaged devices into asmall multi-IC chip assembly package operable at high speeds.

[0004] 2. Description of the Related Art

[0005] The evolution of the computer has resulted in a requirement forgreatly increased memory capacity in much smaller packages. Anotherrequirement is the capability for reliable operation at much higherclock speeds, e.g., up to 800 MHZ or more. In addition, the memorydevice(s) must be readily produced in high quantity and at low cost withreduced rates of failure or rejection. One way to provide a greatermemory storage capacity in a smaller space is by stacking a plurality ofmemory chips and interconnecting them to produce a limited number ofconnections to, e.g., a circuit board. In so doing, a number of factorsmust be addressed, including heat dissipation, ease of interconnection,impedance effects, etc.

[0006] Combining two or more semiconductor dice or chips in a singlesemiconductor device assembly has been used to reduce the space requiredfor integrated circuits. Such devices are generally known as multi-chipmodules (MCM). In one form, dice are stacked vertically on oppositesides of a substrate, for example, or atop each other with interveninginsulative layers, prior to encapsulation. Examples of such devices areshown in U.S. Pat. No. 5,239,198 to Lin et al., U.S. Pat. No. 5,323,060to Fogal et al. and U.S. Pat. No. 5,495,398 to Takiar et al.

[0007] U.S. Pat. No. 5,604,377 discloses a rack with multiple shelvesfor holding unpackaged chips. The chips are electrically connected bylead frames to a wiring interface on a vertical circuit board which canbe connected to a PCB. The entire assembly is contained in a sealedenclosure.

[0008] In U.S. Pat. No. 5,602,420 to Ogata et al., multiple unpackageddice having peripheral bond pads are spacedly stacked, and correspondingbond pads are soldered with meltable balls to one of a plurality ofmetal leads perpendicular to the dice. The active surfaces of the dicemay be coated with an insulative layer after lead bonding, and/or theentire multi-die device may be encapsulated.

[0009] U.S. Pat. No. 5,637,912 discloses a multi-chip module in whichchips are stacked in a vertical arrangement, and a metallization patterndeposited on a surface formed by the chip edges.

[0010] MCM devices are also made which combine a number of diceside-by-side on a substrate. The conventional single in-line multi-chipmodule (SIMM) and dual in-line multi-chip modules (DIMM) are commonexamples of this MCM configuration. Other examples are shown in U.S.Pat. No. 5,137,836 to Lam, U.S. Pat. Nos. 4,992,849 and 4,992,850 toCorbett et al., U.S. Pat. No. 5,255,156 to Chang, U.S. Pat. Nos.5,239,747 and 5,461,544 to Ewers, U.S. Pat. No. 5,465,470 toVongfuangfoo et al., and U.S. Pat. No. 5,480,840 to Barnes et al.

[0011] U.S. Pat. No. 5,592,019 to Ueda et al. shows multiple single-chippackages connected on end to a substrate by their leads.

[0012] The y-axis stacking of multiple packaged devices has been used inan effort toward miniaturization. In U.S. Pat. No. 5,155,067, amulti-chip package is shown wherein packaged devices are stacked in ahousing and sealed with a covering lid. The outer leads of the devicesare connected by, e.g., solder to conductive pads on the housing, andthe pads are attached to, e.g., DIP style leads for attachment to acircuit board.

[0013] A stackable carrier for chips is shown in U.S. Pat. No. 4,996,587to Hinrichsmeyer et al. A single chip or die is adhesively positioned inan underside recess in the carrier and conductive wires from the die arepassed through a hole and bonded to conductors formed on the uppersurface of the carrier. S-shaped connector clips are soldered to each ofthe I/O on the opposed edges of the carrier and to the clips of othercarriers stacked with it to form a multi-chip package (MCM).

[0014] In U.S. Pat. No. 5,514,907 to Moshayedi, a multi-chip memorymodule has a plurality of stacked IC devices between opposing “sideboards,” the latter comprising circuit boards with a pattern ofinterconnected vias into which the pins of the devices are soldered. Thepins of the lowermost device are also soldered to the substrate, such asa main circuit board and comprise the interconnection between the moduleand the circuit board.

[0015] U.S. Pat. No. 5,420,751 to Burns discloses a stacked IC packagewhich has vertical metal rails which pass through a cap above thepackaged devices. Each rail is soldered to corresponding outer leads ofthe primary packages and has a lower end connectable to a PCB. Theprimary devices are adhesively joined to prevent movement of the devicesin the stack package. Manufacture of the rails is a complex process, andthe manipulation of a large number of parts to form the multi-IC packagemay be counterproductive.

[0016] In a later issued patent to Burns, U.S. Pat. No. 5,484,959, astack package for thin small outline package (TSOP) devices is shownwith vertical metal rails for each set of corresponding outer leads ofthe TSOP devices. A secondary “lead frame” for each TSOP package hassecondary leads which are soldered to the pins of the TSOP package andto the metal rails. Each secondary lead is particularly formed with a“flex offset” to provide a stress relief connection with the rail.

[0017] As disclosed, the Burns apparatus requires a second lead framefor each packaged primary device. Furthermore, additional steps arerequired to form the stress relief offset. Furthermore, maintaining therails in parallel non-contact alignment during and following solderingappears to be a major problem. A large number of soldering steps isrequired to join the large number of parts.

[0018] The aforementioned prior art patents disclose multi-chipapparatuses which are deficient in one or more of the following (orother) aspects:

[0019] a. The multi-chip module is complex to make, using a large numberof parts which must be formed, aligned and individually secured in thedevice.

[0020] b. The y-dimension (perpendicular to the host PCB) of themulti-chip module is relatively great, and may be excessive for theparticular end use.

[0021] c. Removal and replacement of a flawed primary device in themodule is extremely difficult and may exceed the value of the module.

[0022] d. The inability to pre-test each primary device prior toincorporation into the multi-chip module results in an increased failurerate in the final multi-chip device.

[0023] e. The leads and connections result in excessive impedanceeffects at high clock speeds, i.e., greater than about 400 MHZ, andparticularly at speeds now anticipated, i.e., about 800 MHZ and higher.

[0024] Among the many considerations in constructing semiconductordevices is thermal expansion. With multi-chip devices in particular,elasticity is required in the electrical connections to accommodatethermal expansion, as well as dimensional variation in the primarydevices.

[0025] U.S. Pat. No. 5,600,183 to Gates, Jr. discloses a conductiveadhesive comprising a mixture of, e.g., silver powder in an epoxymaterial.

[0026] U.S. Pat. No. 5,468,655 to Greer discloses a temporary electricalconnection comprising a metal paste applied to contact pads, then heatedto partially melt the metal. A solder bump may then be placed in contactwith the metal paste and heated to join the bump thereto.

BRIEF SUMMARY OF THE INVENTION

[0027] The present invention comprises a stack package connector bywhich a stack of primary packaged semiconductor devices is joined toprovide a secondary package which is joinable to a printed circuit boardor other host apparatus. In the invention, equivalent outer leads of theprimary packages are joined by flexible conductive buses having lowimpedance and induction effects. One end of each bus is directlyconnectable to contact pads or other contact means of a host printedcircuit board (PCB) or other electronic apparatus.

[0028] In one aspect of the present invention, a plurality ofencapsulated integrated circuit packages is adhesively joined to providea stack to provide one or more planes in which corresponding outer leadsare positioned in vertical alignment. The outer leads of each IC packageare cut close to the package bodies. Conductive buses are formed to joincorresponding outer leads of the packages and terminate in bus endsjoinable to, e.g., a PCB (printed circuit board).

[0029] In one form of conductive bus, an elongate Y-axis conductor tapeis formed of a non-conducting material having parallel linear conductiveelements, i.e., buses, formed to span the tape. On one side of the tape,the conductor ends are configured to enable ready connection to buslines of a circuit board. The width of the tape may be varied toaccommodate different numbers of stacked packages of differingthicknesses in the stack package. The buses of the tape are joined tothe exposed outer leads of the primary packaged devices, typically in asingle step utilizing pressure, conductive adhesive and/or other method.The polymer portion of the tape between the buses may further have anadhesive surface for adhesion to the stacked devices.

[0030] In another form of conductive bus, the stack is placed on acircuit board with conductive pads and a thin stream of conductiveadhesive material such as a metal containing epoxy is applied tocorresponding outer leads and a conductive pad to form a conductive bus.

[0031] In another aspect of the invention, a hollow cage is formed forcontaining the stacked packaged devices. In one embodiment of theinvention, a pattern of bus traces is formed on a “flex PCB” andattached to one inner wall of the cage. Each bus trace terminates in atab or lead end which is attachable to a host circuit board. The outerleads of packages stacked in the cage are bent to provide a degree offlexibility, and the flex PCB may be attached to the cage wall with anelastomeric adhesive to provide additional resiliency for accommodatingvariations in package dimensions. The packages are stacked in the cagewith friction fit, i.e., without being adhesively joined to each otherand having the outer leads simply contacting the bus traces withoutbeing joined to them by solder or other joining means. Thus, the primarypackaged devices may be individually removed and replaced withoutdesoldering or other disjoining step.

[0032] In a further embodiment of the present invention, the cage isformed such that the primary packages have their major planar surfacesaligned at right angles to the surface of the host PCB. The single planeof outer leads is placed against and joined to conductive pads on thesurface of the host PCB. Thus, each outer lead may be joined to aconductive pad. In an alternate version, the PCB is formed with a seriesof elongate conductive pads. The equivalent outer leads of all primarypackages may be joined as a set to a single elongate pad of the PCB.

[0033] In this description, the terms “chip” and “die” are usedinterchangeably. In addition, the term “primary packaged device” refersto an encapsulated package containing one or more dice, each typicallyconnected to a conductive lead frame having outer leads or pins. Suchpackaged devices are typically identified as small outline J-lead (SOJ),thin small outline packages (TSOP), plastic leaded chip carrier (PLCC),single in-line plastic (SIP), dual in-line plastic (DIP), and otherdescriptive names. The term “secondary packaged device” refers to adevice formed by combining a plurality of primary packaged devices in asingle module and interconnecting the primary devices to provide asingle set of electrodes connectable to a circuit board or other hostelectrical apparatus.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0034] The invention is illustrated in the following figures, whereinthe elements are not necessarily shown to scale and certain features maybe exaggerated in dimension:

[0035]FIG. 1 is a perspective view of a low profile multi-IC chippackage incorporating a package connector of the invention;

[0036]FIG. 2 is a cross-sectional view of a package connector for a lowprofile multi-IC chip package of the invention, as taken along line 2-2of FIG. 8;

[0037]FIG. 3 is a cross-sectional view of another embodiment of packageconnector for a low profile multi-IC chip package of the invention, astaken along line 2-2 of FIG. 8;

[0038]FIG. 4 is a cross-sectional view of a further embodiment ofpackage connector for a low profile multi-IC chip package of theinvention, as taken along line 2-2 of FIG. 8;

[0039]FIG. 5 is a cross-sectional view of an additional embodiment ofpackage connector for a low profile multi-IC chip package of theinvention, as taken along line 2-2 of FIG. 8;

[0040]FIG. 6 is a cross-sectional view of another embodiment of packageconnector for a low profile multi-IC chip package of the invention, astaken along line 2-2 of FIG. 8;

[0041]FIG. 7 is a side view of a Y-axis conductive tape of a packageconnector of the invention;

[0042]FIG. 8 is a top view of a Y-axis conductive tape of a packageconnector of the invention;

[0043]FIG. 9 is a perspective view of another embodiment of a lowprofile multi-IC chip package incorporating a package connector of theinvention;

[0044]FIG. 10 is a partial end view of a low profile multi-IC chippackage illustrating the formation of an electrical bus of a connectorthereof;

[0045]FIG. 11 is a plan view of a further embodiment of a low profilemulti-IC chip package incorporating a package connector of theinvention;

[0046]FIG. 12 is a cross-sectional side view of an embodiment of a lowprofile multi-IC chip package incorporating a package connector of theinvention, as taken along line 11-11 of FIG. 11; and

[0047]FIG. 13 is a cross-sectional side view of another embodiment of alow profile multi-IC chip package incorporating a package connector ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

[0048] An improved low profile, high speed multi-IC chip connector andresulting stack package for memory chips is provided by the presentinvention. Different embodiments of the connector are illustrated in thedrawing figures. The connector is joined to a stack of encapsulatedsemiconductor devices, each of which comprises a primary packagecontaining one or more electrically connected dice. Preferably, eachpackage has been burned-in and tested prior to joining to the connectoras part of a stack. The stack package typically comprises at least twoprimary packages, although the number of packages is more normally about4 to 8, or more. Any number of primary packages may be incorporated in asecondary package, limited only by such considerations as spacerequirements, the effect of bus length upon impedance, and the like.Additionally, the secondary package is suitable for use of primarypackages having clock speeds of at least 400 MHZ, 800 MHZ, or greater.

[0049] The various embodiments of the invention are particularlyapplicable to high-speed memory packages such as are required to achieveprocessing speeds of 800 MHZ or higher.

[0050] The speed capability of prior art memory chips has lagged thecapability of RAM (random access memory) chips, and has been asignificant limiting factor in the production of high speed computersand the like for operation at clock speeds of 600 MHZ and higher. Thisinvention may be particularly applied to the advancement of memorychips, replacing current SIMM and DIMM module designs which areinadequate.

[0051] Turning now to drawing FIG. 1, one embodiment of a multi-chippackage 10 of the invention is illustrated. The multi-chip package 10 isshown with a stack 12 of four primary semiconductor packaged devices 14,also simply called “primary packages” herein, such as are well known inthe art. Each primary package 14 contains at least one semiconductor diehaving interconnections such as by a lead frame to a plurality of outerleads 16. The semiconductor die and lead frame are not visible in thedrawing figures, being within the protective layer of, e.g., insulativepolymer on the exterior of each primary package 14. Each primary package14 is shown with major upper and lower surfaces 18 and 20 which areconnected by ends 22, 24 and lateral edges 26 and 28. Truncated outerleads 16 are shown extending outwardly from each of lateral edges 26 and28, respectively. The primary packages 14 are joined to each other andto a host circuit board 30 by nonconductive adhesive material 32, whichmay be a tape such as Kapton polyimide, or a flowable adhesive cement.Circuit board 30 is shown with electrically conductive pads 34 forconnection to the multi-chip package 10.

[0052] The primary packages 14 are electrically joined by a flexibleconnector 36, details of which are shown in drawing FIGS. 1-8.

[0053] The connector 36 comprises a layer 38 of insulative polymericmaterial such as Kapton polyimide. On one side 42 of the polymeric layer38 is superposed a series of parallel conductive buses 40. The buses 40are spaced on the polymeric layer 38 to match the spacing of the outerleads 16. The buses 40 may be metal wire of varied cross-sectionalshapes and adhesively joined to the polymeric layer 38.

[0054] Shown in drawing FIGS. 2-6 are five exemplary configurations ofbus 40 which may be used in the connector 36. Other shapes may also beused. The bus may be a simple round wire 40A attached with adhesive 44to side 42 of the polymeric layer 38, as shown in FIG. 2. The pitch 48of the wires 40A is controlled to equal the spacing or pitch of theouter leads 16. Side 54 of the polymeric layer 38 is the externalsurface of the connector 36.

[0055] In drawing FIG. 3, a semi-round wire 40B is depicted, and drawingFIG. 4 shows a flat wire 40C attached with adhesive 44. As depicted indrawing FIG. 5, a flat wire 40D with side grooves 46 for enhancing theattachment forces of the wire to the polymeric layer 38 with adhesive 44is shown.

[0056] Where the polymeric layer 38 is a thermoplastic, the bus 40B maybe attached to the polymeric layer 38 by heating the wire and pressingit into the layer. As shown in drawing FIG. 6, the wire 40E may have ashape which includes a lock 50 which is embedded in the polymeric layer38 for firmly attaching the wire to the polymeric layer. The wire 40Emay be heated by passing an electric current through the wire.

[0057] As depicted in drawing FIG. 1, the flexibility of the connector36 permits conformation to the rows of outer leads 16 and the lateraledges 26, 28 of the primary packages 14. The bending of the connector 36is exaggerated in FIG. 1 for better comprehension. Use of the connector36 of drawing FIG. 1 permits formation of a four-package multi-chippackage device 10 having an overall height 64 (FIG. 12) of about 6 mm orless.

[0058] The polymeric layer 38 of the connector 36 may have a typicalthickness 52 (FIG. 2) of about one (1) to about five (5) mils, and ispreferably formed of polyimide, although other suitable polymers may beused. The buses 40 have cross-sectional dimensions such that theimpedance and inductance are sufficiently low to enable high qualityoperation at the specified clock speed and power rating. For example, ina multi-chip device of four primary memory packages, a suitable roundaluminum wire 40A provides acceptable conductance and impedance.

[0059] In a preferred embodiment, the outer leads 16 of the primarypackages 14, as well as the buses 40, have a uniform pitch, i.e.,spacing.

[0060] As shown in drawing FIG. 1, the buses 40 of connector 36 areattached to the outer leads 16 of the primary packages 14 such that theequivalent outer leads of the packages are attached to the same bus.Each bus 40 has one end 56 which is attachable to a conductive pad 34 ofthe host circuit board 30. The bus-to-lead and bus-to-pad connectionsmay be made with heat, e.g., a low temperature solder, by pressure, orwith application of a conductive adhesive, or by any suitable well knownconnection methods in the art.

[0061] As depicted in drawing FIGS. 7 and 8, the connector 36 may beformed as a semicontinuous tape 58 with transverse buses 40 attached tothe polymeric layer 38, e.g., Kapton™ polyimide. The tape 58 may bepre-manufactured to provide the desired bus configurations, pitch 48 andtape widths 60 applicable to a manufacturer's product line. The tape 58is cut to fit each multi-IC chip package. As shown, the tape may beplaced on a spool 62 for easy dispensing and use. Alternately, aflex-circuit 58 having transverse buses 40 secured to an etchedpolymeric layer 38 exposing the buses 40 may be used.

[0062] In another embodiment of the invention shown in drawing FIG. 9, amulti-IC chip package 10 is shown with a stack 12 of primary packages 14as previously described. The outer leads 16 of the primary packages 14are truncated to extend only a short distance outward from the packages.The connector 36 comprises a series of buses 40 formed of a flowableconductive material which sets to a hard but flexible conductor capableof high conductance, low impedance performance. The conductive materialof the buses 40 may be a polymer, e.g., epoxy, containing smallparticles of conductive metal, i.e., silver, gold or aluminum.Alternatively, the bus material may be a polymer having sufficientconductance and low impedance for high-speed operation. Examples ofconductive polymers include doped polyacetylene, polypyrrole,polythiophene and polyaniline. The dopant is selected to provide thedesired electrical properties and may be, for example, iodine. Thematerial may be selected to set upon a change in temperature or byradiation, for example. If necessary, chemical agents for retarding orenhancing the setting speed may be included in the polymer formulation.

[0063] As shown in drawing FIG. 10, each bus 40 is formed by passingconductive polymer 66 with a controlled setting rate in a minute stream68 from an outlet 74 of a polymer extruder 70. The extruder is moved upand/or down in a vertical direction 72 and in a horizontal direction 76to join the equivalent outer leads 16 of the primary packages 14 withthe conductive pads 34 of the host circuit board 30. The bus 40 is builtup to the desired cross-section for optimal device performance. Aplurality, or even all of the buses 40, may be formed simultaneouslyusing a polymer extruder 70 with multiple outlets 74.

[0064] In the embodiments of drawing FIGS. 1-10, the multi-IC chippackage is adaptable to stacks 12 of primary packages 14 having outerleads 16 on one, two, three or four sides. The stack 12 may comprise twoor more primary packages 14, but typically will comprise about fourpackages, each with outer leads 16 on one or two sides.

[0065] Another embodiment of the invention is depicted in FIGS. 11 and12. The multi-IC chip package 80 has a stack connector 82, illustratedas comprising a cage 84, for holding by friction an exemplary stack 86of eight primary packages 14. The cage 84 is shown to contact a portionor portions of lateral edge 26 of each primary package 14, and closelyapproach or contact the package ends 22, 24. The cage 84 partiallyencloses the primary packages 14 to retain them as a stack. The cage 84may be formed of a thin metal sheet, a strong polymeric material,ceramic, or the like. The cage 84 is most easily formed from a metalsheet, extruded metal, extruded plastic, molded plastic, thermoplastic,etc., typically of five (5) to one hundred (100) mils thickness 100,which is cut and bent at 90 degrees at each of the four corners 102,104, 106, and 108, forming the five panels 110, 112, 114, 116 and 118. Agap 120 between coplanar panels 116 and 118 permits easy removal ofprimary packages 14 from the cage 84. Particularly when formed of metal,the high heat conductivity of the cage 84 results in enhanced heatdissipation from the multi-IC chip package or module 80 during use. Thecage 84 also acts as a heat sink to minimize temperature variations ofthe primary packages 14.

[0066] On one interior wall 88, herein called the “active wall” of thecage 84, a thin “flex PCB” 92 is attached by a layer 94 of elastomericadhesive. The thickness 96 of the adhesive layer 94 is controlled toprovide a desired degree of flexibility. Buses 90 are formed on the flexPCB 92 with a pitch 48 matching the pitch 49 of the outer leads 16, andare positioned to contact the sets of corresponding outer leads 16 ofthe primary packages 14 when they are inserted into the cage 84. Thebuses 90 may be metal strips attached to the flex PCB 92 by adhesive,not shown, or may be formed by metallization and lithographic busseparation, for example. If desired, the outer leads 16 of the primarypackages 14 may be soldered to the buses 90 or connected to the buses 90using suitable conductive material.

[0067] The lower end 124 of each of the buses 90 is shown as comprisinga horizontal portion insulated from the cage 84 by non-conductiveelastomeric adhesive layer 94. The lower end 124 may be attached to aconductive pad or lead 34 of the host circuit board 30 by methodswell-known in the art, e.g., by surface mounting with solder, bondingwith conductive adhesive, and the like.

[0068] The thin flex PCB 92 and elastomeric adhesive layer 94 provideresilience by which variations in dimensions of the primary packages 14and their buses 90 are accommodated. Typically, the thickness 98 of theflex PCB 92 is about one (1) to five (5) mils, and the thickness 96 ofthe adhesive layer is about three (3) to eight (8) mils, but thicknesseslesser or greater than these values may be used.

[0069] As shown, the outer leads 16 of the primary packages 14 are bentto flex with compressive forces imposed by the cage 84, flex PCB 92 andelastomeric adhesive layer 94. Thus, the electrical connections aremaintained by compression and friction. The primary packages 14 may beeasily inserted and extracted merely by pulling them from the cage 84.Desoldering or other steps of heating, cutting, etc. are not required toremove a primary package 14.

[0070] Where sharp forces on the host circuit board 30 may loosen aprimary package 14 within the cage 84, a small dab(s) of adhesive may beused to fix the topmost primary package 14 to the cage. The adhesive maybe easily removed if necessary to replace a primary package.Alternatively, a small node or nodes 122 of polymeric material may beformed on one or more cage panels 110, 112, 114, 116 and 118 to providean additional resistance to removal of any primary package 14. The nodesmay be ribs 122 which conform to the shape of primary packages 14 tomaintain the entire exemplary stack 86 immobile during use, yet alloweasy removal.

[0071] In an example of this embodiment, a multi-IC chip package 80 witheight typical primary packages 14 eight-hundred (800) mils in length andfour-hundred-fifty (450) mils in width may have an overall height ofless than about ten (10) mm. This embodiment of a multi-IC chip package80 is most aptly applied to primary packages 14 having outer leads 16along one side only. However, two opposing flex PCB members 92 withbuses 90 could be attached to opposing inner walls of a cage 84 toaccommodate primary packages 14 with outer leads 16 along both opposinglateral edges 26 and 28.

[0072] In use, the cage 84 with attached flex PCB 92 and buses 90 isattached to the host circuit board 30 with adhesive and the bus lowerends 124 are soldered or otherwise attached to the conductive pads orleads 34 of the host circuit board 30. The primary packages 14 are theninserted and pushed downwardly within the cage 84 to form an exemplarystack 86, the outer leads 16 of each primary package compressed slightlyduring the insertion step.

[0073] The footprints of the multi-IC chip packages 10 and 80 are onlyslightly larger than the footprint of a primary package 14 which isstacked in packages 10 and 80. Thus, the density is considerably greaterthan the SIMM and DIMM packages currently in use. The number of primarypackages 14 which may be incorporated in the stack is typically eight ormore, but fewer than eight may be used.

[0074] Another embodiment of the multi-IC chip package is illustrated indrawing FIG. 13. This multi-IC chip package 130 is similar to thepackage 80 of drawing FIGS. 11 and 12, except that the cage 132 has butthree full panels and has no flex PCB or buses. The cage 132 is rotatedrelative to cage 84 of package 80 so that the outer leads 16 of theprimary packages 14 may be directly attached to conductive pads orelongate leads 34 of the host circuit board 30 without an interveningpanel. The primary packages 14 have their major upper and lower surfaces18, 20 in a vertical attitude and are stacked horizontally. Thus, theheight dimension 134 is the same regardless of the number of primarypackages 14 in the stack. The two opposed cage walls are attached to thehost circuit board 30, e.g., by adhesive 136 or other means, such assnap pins, not shown in drawing FIG. 13, which are fitted into holes inthe host circuit board 30. Alternately, the cage 132 may be soldered tothe circuit board 30.

[0075] Small ribs 122 may be incorporated into inner walls of the cage132 to provide resistance to removal of the primary packages 14 from thecage.

[0076] The footprint of the multi-IC chip package 130 is only slightlylarger than the footprint of a primary package 14 which is stacked inpackages 10 and 80. Thus, the density is considerably greater than theSIMM and DIMM packages currently in use.

[0077] The invention provides for the use of buses which are relativelyshort and of enhanced cross-section to produce low impedance at highclock speeds, i.e., up to 800 MHZ, and relatively high power ratings.The multi-IC chip packages are easy to produce with high accuracy.Primary packages using well-developed technologies and having pretestedhigh reliability are used in the stacks. The invention is applicable tohigh speed memory modules which are to supersede the SIMM and DIMMpackages.

[0078] As indicated in the foregoing, each embodiment of the multi-ICchip package of the invention has particular advantages under particularcircumstances.

[0079] It is apparent to those skilled in the art that various changesand modifications may be made to the multi-IC chip stacked package andpackage connector thereof in accordance with the disclosure hereinwithout departing from the spirit and scope of the invention as definedin the following claims.

What is claimed is:
 1. A method for connecting a vertically stackedplurality of primary integrated circuit packages on a substrate having aplurality of circuits thereon, each primary integrated circuit packagehaving a plurality of outer leads and having a plurality of sides, usinga tape of polymeric material having a width, comprising: forming aplurality of spaced transverse conductive buses on said non-conductivepolymeric material, at least one conductive buses of said plurality ofconductive buses having one end for connection to an electricallyconductive pad of said substrate; connecting said at least one bus ofsaid plurality of spaced transverse conductive busses to at least onelead of said outer leads of said stacked plurality of primary integratedcircuit packages and to at least one circuit of said plurality ofcircuits of said substrate; providing a cage enclosing at least twosides of said plurality of sides of each primary integrated circuitpackage of said stacked plurality of primary integrated circuitpackages; and attaching said cage to said substrate, said cageconnecting at least one outer lead of said outer leads of said stackedplurality of primary integrated circuit packages to at least oneconductive bus of said plurality of spaced transverse conductive buses.2. The method of claim 1, wherein said flexible non-conductive polymericmaterial comprises polyimide.
 3. The method of claim 1, wherein said atleast one bus of said plurality of spaced transverse conductive busescomprises one of a round, a semi-round and a rectangular wire portionattached to said non-conductive polymeric material by a non-conductivepolymeric adhesive.
 4. The method of claim 1, wherein said at least onebus of said plurality of spaced transverse conductive buses comprises awire portion having projections for locking attachment to saidnon-conductive polymeric material by a non-conductive polymericadhesive.
 5. The method of claim 1, wherein the width of saidsemi-continuous tape includes at least four primary packages.
 6. Themethod of claim 1, further comprising: providing a cage enclosing morethan at least two sides of said plurality of sides of each primaryintegrated circuit package of said stacked plurality of primaryintegrated circuit packages; and attaching said cage to said substrate,said cage connecting at least one outer lead of said outer leads of saidstacked plurality of primary integrated circuit packages to at least oneconductive bus of said plurality of spaced transverse conductive buses.7. The method of claim 6, wherein a portion of said semi-continuous tapeis located within said cage, and a portion of at least one conductivebus of said plurality of spaced transverse conductive buses contacts atleast one outer lead of said outer leads of said stacked plurality ofprimary integrated circuit packages and at least one conductive bus ofsaid plurality of spaced transverse conductive buses.
 8. A method forconnecting a vertically stacked plurality of primary integrated circuitpackages on a substrate having a plurality of circuits thereon, eachprimary integrated circuit package having a plurality of outer leads andhaving a plurality of sides, using a flexible tape of non-conductivepolymeric material having a width, comprising: forming a plurality ofspaced transverse conductive buses on said non-conductive polymericmaterial, at least one conductive buses of said plurality of conductivebuses having one end for connection to an electrically conductive pad ofsaid substrate; connecting said at least one bus of said plurality ofspaced transverse conductive busses to at least one lead of said outerleads of said stacked plurality of primary integrated circuit packagesand to at least one circuit of said plurality of circuits of saidsubstrate; providing a cage enclosing at least two sides of saidplurality of sides of each primary integrated circuit package of saidstacked plurality of primary integrated circuit packages; and attachingsaid cage to said substrate, said cage connecting at least one outerlead of said outer leads of said stacked plurality of primary integratedcircuit packages to at least one conductive bus of said plurality ofspaced transverse conductive buses.
 9. A method for connecting avertically stacked plurality of primary integrated circuit packages on asubstrate having a plurality of circuits thereon, each primaryintegrated circuit package having a plurality of outer leads and havinga plurality of sides, using a semi-continuous flexible tape of polymericmaterial having a width, comprising: forming a plurality of spacedtransverse conductive buses on said non-conductive polymeric material,at least one conductive buses of said plurality of conductive buseshaving one end for connection to an electrically conductive pad of saidsubstrate; connecting said at least one bus of said plurality of spacedtransverse conductive busses to at least one lead of said outer leads ofsaid stacked plurality of primary integrated circuit packages and to atleast one circuit of said plurality of circuits of said substrate;providing a cage enclosing at least two sides of said plurality of sidesof each primary integrated circuit package of said stacked plurality ofprimary integrated circuit packages; and attaching said cage to saidsubstrate, said cage connecting at least one outer lead of said outerleads of said stacked plurality of primary integrated circuit packagesto at least one conductive bus of said plurality of spaced transverseconductive buses, a portion of said semi-continuous tape located withinsaid cage.